DermatologyTier 2Approach to a presentation

Ulcers - genital

Red flags

Concurrent systemic symptoms (fever, lymphadenopathy suggesting disseminated infection), signs of necrotising soft tissue infection (rapidly spreading pain out of proportion, crepitus, systemic toxicity), and ulceration in an immunocompromised host warranting more urgent/aggressive assessment

Differential by mechanism

Infective: herpes simplex virus (painful, grouped vesicles/ulcers), syphilis (painless chancre), chancroid (painful, ragged ulcer, rare in most high-income settings), lymphogranuloma venereum

Non-infective: Behcet disease (recurrent oral and genital ulceration), fixed drug eruption, trauma, malignancy (rare but important in an atypical or non-healing ulcer)

Focused history

Ulcer onset, pain (a key discriminator - HSV and chancroid are painful, syphilis is classically painless), number and evolution of lesions (vesicles preceding ulcers suggests HSV)
Sexual history (partners, protection use, prior STI history), systemic symptoms (fever, rash, lymphadenopathy), recurrence pattern (recurrent painful ulcers with prodrome suggests HSV; recurrent oral plus genital ulcers suggests Behcet)

Focused examination

Direct inspection: number, depth, base appearance (clean vs ragged/necrotic), tenderness, and inguinal lymphadenopathy (tender/fluctuant suggesting chancroid or LGV, non-tender suggesting syphilis)
Full skin and mucosal examination for associated findings (oral ulcers - Behcet; rash - secondary syphilis)

Investigation strategy

HSV PCR/viral swab from the ulcer base (preferred over older viral culture for sensitivity)
Syphilis serology (treponemal and non-treponemal tests) and dark-field microscopy/PCR of chancre fluid where available
Full STI screen (given high rates of co-infection), HIV testing (offered as part of standard STI screening given shared risk factors)

Management

HSV: aciclovir/valaciclovir - episodic for a first or infrequent recurrence, suppressive therapy for frequent recurrences; partner notification and counselling regarding transmission risk (including during asymptomatic shedding)
Syphilis: benzathine penicillin (stage-dependent dosing); notifiable disease with partner notification and contact tracing
Behcet-associated ulceration: topical/systemic immunosuppression guided by overall disease severity, coordinated with rheumatology

Traps

Painless does not mean benign - a painless chancre (primary syphilis) is easily dismissed or missed, yet requires urgent treatment and partner notification

Missing co-infection - genital ulcer disease substantially increases HIV acquisition/transmission risk, making HIV testing an essential accompaniment, not an afterthought

Assuming a single cause - concurrent HSV and syphilis, or other STI co-infection, is not rare in sexually active patients presenting with an ulcer

Talk track

"This looks like it could be one of a few different infections - I'd like to take a swab from the ulcer and do some blood tests, including a full sexual health screen, so we get the right treatment and can also let any partners know if needed."

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